Process of treating coiled articles



Aug. 7, 1962 F. M. DE BRITZ ET AL 3,043,200

PROCESS OF TREATING COILED ARTICLES Filed March 12, 1958 FIG.|.

FIG. 8.

FIG.4.

FIG.5.

FIG.6.

FIG. 7.

TIME IN MINUTES INVENTORS FRANCIS M.DeBR|TZ ALVIN A. WISCO.

ATTORNEY 2 dimension tolerance.

United States Patent ()fifice Patented Aug. 7, 19552 PROCESS OF TREATING COILED ARTICLES Francis M. de Britz, Brooklyn, N.Y., and Alvin A. Wisco,

Kinnelon, N.J., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Mar. 12, 1958, Ser. No. 720,919 6 Claims. (Cl. Mil-71) This invention relates to the manufacture of coiled articles and, more particularly, to a process of treating tungsten filaments of the type employed in automobile headlamps and the like.

In order to facilitate the mounting of certain types of incandescent lamp filaments, it has become the practice to leave uncoiled sections at each end of the coil during the coil winding operation and then bend these sections transverse to the axis of the coil to provide accurately oriented depending end sections or so-called legs. Mounting filaments of this character is accomplished by anchoring the leg portions to appropriately spaced supporting means, such as the lamp lead-in wires or the like, which members are so disposed that the coiled body portion of the mounted filament is properly located within the lamp or, as in the case of an automobile headlamp, oriented in precise predetermined relationship with the reflector portion of the lamp.

Insofar as filaments of this type are generally mounted automatically, it is essential that the leg portions be properly spaced and so positioned angularly with respect to each other on opposite sides of the longitudinal bisectional plane of the filament that they are in substantial alignment with the supporting members in order to insure that both leg portions are properly attached to the supporting members and to prevent deleteriously distorting or displacing the coiled body portions of the filaments during the mounting operation. The angular alignment of the leg portions with respect to one another on either side of said plane is very critical due to the nature of the automatic mounting operation and for this reason displacement of the legs from the position which would exactly align them with the supporting members must be held within preselected limits or a so-called offset leg Due to the fact that relatively minor variations in the coiling process introduce large deviations in the angular disposition of the leg portions before and after bending, it is very difficult to maintain the offset leg dimension within the limits required to satisfactorily and properly mount the filaments automatically without excessive shrinkage. It has, therefore, been necessary to carefully inspect the finished filaments and either reject those which are not within the limits defined by the preselected offset leg dimension tolerance or manually adjust the legs to meet this tolerance thereby drastically increasing the percent shrinkage and the cost of such filaments as compared to conventional types of filaments.

It is accordingly the general object of the present invention to obviate the foregoing deficiencies inherent in the prior art method of fabricating coiled articles requiring accurately oriented transversely-extending leg portions.

Another and more specific object of this invention is to provide a process for accurately positioning the leg portions of coiled refractory wire filaments which process will not only lend itself to mass production techniques and facilitate the coil-winding operation but which will effect the desired positioning with a minimum amount of material, labor and shrinkage.

The aforesaid objects, and others which will become apparent as the description proceeds, are accomplished according to the invention by initially orienting the uncoiled leg portions of the filament at a predetermined angle relative to one another and the longitudinal bisectional plane of the filament such that the offset leg dimension tolerance is greater than that heretofore employed and the resultant angular displacement of said leg portions from their desired position is in the same direction as that which would normally occur if the coiled body portions of the filament were twisted in the direction in which they were wound, and then heat treating the filaments to controllably relieve the residual torsional stresses therein and reposition said leg portions to achieve a spacing there- 'between that falls Within a preselected tolerance established for their alignment.

A better understanding of the invention may be obtained by referring to the accompanying drawing wherein:

FIG. '1 is a front elevational view on an enlarged scale of a tungsten filament adapted for use in an automobile headlamp, which filament is representative of the type of coiled article which may be processed according to this invention;

FIG. 2 is a side view of the filament shown in FIG. 1;

FIGS. 3, 4 and 5 are views corresponding to FIG. 2 but illustrate the desired offset leg dimension tolerance established for filaments of this type to insure satisfactory mounting by a particular type of automatic mounting device and heretofore met by carefully controlling the coiling and leg-bending operations or by manual adjustment of the finished product, the greater or permissible tolerance afforded by the present invention, and the differential tolerance or the difference between the aforesaid desired and permissible tolerances, respectively;

FIG. 6 is a graph illustrating the adjustment in mils in the angular positioning of the leg portions (either in a divergent or convergent direction depending upon the type of filament being processed) versus the length of time the finished filaments are baked in air at about 300 C. in accordance with the preferred stress-relieving schedule of this invention; and

FIGS. 7 to 11 are views corresponding to FIGS. 1 to 5 but illustrate the manner in which the invention would be applied to the type of automobile headlamp filament or similar coiled article which is wound or has its leg portions formed in such a manner that they tend to converge rather than-diverge when the filament is stress-relieved.

While the process hereinafter described may be employed to accurately align the transverse leg portions of any type of coiled article having residual torsional stresses and which is thus capable of being stress-relieved, the invention is especially useful in conjunction with the manufacture of coiled tungsten wire filaments of the type use in automobile headlamps and hence has been so illus.- trated and will be so described.

With specific reference to the drawing, in FIG. 1 there is shown a coiled tungsten wire filament 12 of the aforementioned type. As is well known, such filaments comprise a coiled body portion 14 terminated by uncoiled end sections disposed transverse to the longitudinal axis of the aforesaid coiled body portion to provide a pair of depending leg portions 16 adapted to facilitate the mounting of the filament 12in its position of use within the lamp. In the instant example, the leg portions 16 are disposed normal to the longitudinal axis of the coiled body portion 14 and are longitudinally spaced a predetermined distance from each other so that the spread therebetween is sub stantially equal to that of the lamp lead-in wires or other support means to which they will be attached.

As shown in FIG. 2, the leg portions 16 ideally are disposed parallel to each other when viewed along the longitudinal biseotional plane of the filament 12 and in the instant case are on opposite sides of said plane and spaced or offset a predetermined distance x from each other, which dimension is generally referred to as the offset leg dimension. In the 50 watt automobile headlamp filament here illustrated, the leg portions 16 are offset a distance approximately equal to the outside diameter of the coil barrel or about .060 thereby disposing the aforesaid leg portions in substantial angular alignment with the preformed lamp lead-in wires. In practice, this dimension is measured at a predetermined point just above the divergent tips or so-called feet of the leg portions 16, as viewed in FIGS. 1 to 5, in order to prevent slight irregularities in the disposition of said feet from giving an erroneous measurement.

In order to insure that the filament 12 will be properly anchored to the lead-in wires by the automatic mounting apparatus employed for this purpose, it has been found necessary to maintain the offset leg dimension within a preselected or desired tolerance, as for example from about .045 to about .090" for the type of filament here illustrated, as indicated in FIG. 3. The exact tolerance will, of course, depend upon the particular type of coil and supporting means involved and the automatic mounting equipment utilized. Heretofore, it has been the practice to manufacture the filaments 12 to this desired tolerance by very accurately controlling the coiling and leg-forming operations. However, due to the critical nature of these operations it is very difiicult to angularly position the leg portions 16 within such tight limits resulting in approximately 50% shrinkage in the finished product and requiring very close supervision of the coiling machines by a skilled operator.

In accordance with this invention, the initial offset leg dimension tolerance, that is, the manufacturing tolerance, is increased by a predetermined amount in the same direction as the angular displacement which would normally occur between the leg portions 16 if the coiled body portion 14 of the finished filament were twisted in the direction in which it was wound. Thus, for this particular type of filament the leg portions 16 are initially disposed at such an angle with respect to one another and the longitudinal bisectional plane of the filament 12 that the leg spacing is smaller than that desired, as for example at an angle such that the offset leg dimension tolerance in the case here illustrated is increased at its lower limit by an amount which will permit a greater angular deviation in this direction and thus establish a permissible tolerance of from about .020 to about .090, as-shown in FIG. 4.

After completion of the coiling and leg'forming operations, the filaments 12 are first degreased, as by immersion in trichloroethylene for example, dried by very low heat (slightly above room temperature), and then inspected in accordance with the usual procedure. Those filaments which meet the aforesaid desired offset leg dimension tolerance are used directly in production whereas those within the differential tolerance of about .020" to about .045", that is, the difference between the aforementioned desired tolerance and the permissible tolerance indicated by the shaded area in FIG. 5, are heated to a pre' selected temperature for a predetermined time in accordance with the invention to controllably relieve the residual torsional stresses in the coiled body portion 14 and thus cause the leg portions 16 to swing away from each other and thus diverge or open by an amount snfficient to bring them within the limits defined by the desired toler- 'ance.

As a specific example of a satisfactory stress-relieving or baking schedule, it has been found that when the filaments 12 within the above-mentioned differential tolerance are heated in air to a temperature from about 275 C. to 325 C. (and preferentially to a temperature of about 300 C.) for approximately three minutes, the leg portions 16 will diverge by about .025", as indicated by the graph shown in FIG. 6, thereby bringing all such filaments within the aforementioned desired tolerance. Experience has shown that the finished filaments 12 can be heated in air at this temperature for as long as about 8 minutes without deleteriously oxidizing the filaments.

Moreover, the baking process appears to set the leg portions 16 in the desired angular position relative to one another thereby insuring that said leg portions remain in predetermined angular alignment during storage or shipment.

As indicated by the exponential character of the curve shown in FIG. 6, increasing the time of baking will effect even greater angular adjustments of the leg portions 16 than the .025" correction cited above thereby permitting the permissible offset leg dimension tolerance to be increased by a correspondingly greater increment. It will also be obvious that the time and temperature of baking may be varied over a rather wide range depending upon the type of coiled article being treated, the nature of material from which it is fabricated, and the degree of angular adjustment desiredthe only limitations being that the temperature at all times is maintained Well below the recrystallization temperature of the material (approximately 1200 C. for tungsten) to avoid deleteriously embrittling the articles and that the baking be done in an inert atmosphere such as nitrogen or the like in those instances where the heating schedule selected is such that it would cause excessive oxidation of the parts if they were treated in air.

When the direction of winding or the manner in which the leg portions are formed is such that the natural tendency of the leg portions is to close rather than open, then the initial or manufacturing tolerance is increased by a predetermined amount in the opposite direction. This situation is illustrated in FIGS. 7 to 11 wherein a filament 12a having a coiled body portion 14a of slightly lower wattage rating than the filament 12 referred to above is provided with leg portions 16a which are bent straight back from the aforesaid coiled body portion so as to be offset one from another a distance x, as shown most particularly in FIG. 8, rather than being bent in the reverse manner as in the case of the aforesaid filament 12. In the present instance, therefore, if the coiled body portion 14a were twisted in the direction in which it is wound, the leg portions 16a would tend to diverge rather than converge. Hence, the tolerance to which the filaments are initially formed is shifted toward the high side of the desired tolerance, which for this particular type filament is from about .045" to about .090" (as shown in FIG. 9), preferably by an amount sufficient to provide a permissible" tolerance of from about .060" to about .115" (FIG. 10). Thus, the differential tolerance in this instance would be from about .090" to about .115", as indicated by the shaded angular area of FIG. 11. The filaments 12a found by inspection to be outside the desired tolerance and within the differential tolerance are subjected to a stress-relieving temperature for a sufficient length of time to effect a convergence of the leg portions 16a through an angular distance of about .025" and thus correct for the angular deviation of said leg portions from the desired positioning in the same manner as set forth above.

It will be apparent from the foregoing that the objects of the invention have been achieved insofar as a very convenient and inexpensive process has been provided for accurately aligning the transversely-extending leg portions of a coiled article angularly with respect to one another and the longitudinal bisectional plane of said article by controllably stress-relieving the finished articles en masse without deleteriously embrittling or oxidizing them. When the relaxation in the manufacturing tolerance afforded by this invention may appear relatively small, processing the instant automobile headlamp filaments in accordance with the foregoing procedure has reduced the percent shrinkage from about 50% to approximately 15% which factor, in conjunction with the resultant decrease in the degree of skilled supervision of the winding machines required by the heretofore very critical coiling and leg-forming operations, obviated a contemplated 50% increase in the cost of these filaments.

While several specific embodiments of the heat treating process according to the invention have been illustrated and described in detail in accordance with the patent statutes, it will be understood that these are cited merely by way of example and that various modifications and changes may be made without departing from the spirit and scope of the invention.

We claim:

1. In the manufacture of coiled articles wound from refractory wire and having leg portions at each end which extend transversely from the coiled body portions of said articles, the process of orienting said leg portions in a desired alignment with respect to each other and the longitudinal bisectional plane of the respective ones of said articles, which process comprises initially positioning said leg portions during the formation thereof at angles such that the spacing therebetween and from said plane differs from that desired and the differential is in a direction such that the resultant angular displacement of said leg portions from the desired alignment is in the same direction as would normally occur if the coiled body portions of said articles were twisted in the direction in which they were wound, completing the fabrication of said articles, and then heating the finished articles en masse under controlled time and temperature conditions to relieve the residual torsional stresses in the coiled body portions thereof by an amount sufficient to cause said leg portions to swing into the desired alignment.

2. The process of aligning the leg portions of coiled refractory wire articles as set forth in claim 1 wherein the said finished articles are heated in air at a temperature and for time sufiicient to effect the desired repositioning of said leg portions without deleteriously oxidizing or embrittling said articles.

3. In the manufacture of a tungsten wire filament which has a coiled body portion and uncoiled leg portions which extend transversely from each end of said body portion, the process of orienting said leg portions in a desired alignment on opposite sides of the longitudinal bisectional plane of said filament, which process comprises relaxing the manufacturing tolerance of said filaments to permit said leg portions to be positioned during the formation thereof at angles such that the spacing therebetween initially differs from that desired and the difierential is in a direction such that the resultant angular displacement of said leg portions from the desired alignment is in the same direction as would normally occur if the coiled body portion of said filament were twisted in the direction in which it was wound, completing the fabrication of said filament, and then heating the finished filaments en masse to a temperature well elow the recrystallization temperature of tungsten to relieve the residual torsional stresses in the coiled body sections of said finished filaments by an amount suficient to cause said leg portions to swing into the desired alignment.

4. In the manufacture of a trungsten wire filament which has a coiled body portion and uncoiled leg portions Which extend transversely from each end of said body portion, the process of orienting said leg portions in a desired alignment on opposite sides of the longitudinal bisectional plane of said filament, which process comprises relaxing the manufacturing tolerance of said filaments to permit said leg portions to be positioned during the formation thereof at angles such that the spacing therebetween initially differs from that desired and the differential is in a direction such that the resultant angular displacement of said leg portions from the desired alignment is in the same direction as would normally occur if the coiled body portion of said filament were twisted in the direction in which it was wound, completing the fabrication of said filaments, and then heating the finished filaments en masse in air to a temperature from about 275 C. to 325 C. for a period not exceeding about 8 minutes thereby to relieve residual torsional stresses in the coiled body sections of said finished filaments and cause said leg portions to swing into the desired alignment before said filaments become deleteriously oxidized.

5. In the manufacture of coiled refractory wire filaments having a coiled body portion and transversely extending uncoiled leg portions at each end for anchoring said filaments to spaced supporting members, the process of aligning said leg portions with respect to the longitudinal bisectional plane of the respective filaments within a first tolerance selected to facilitate the attachment of said leg portions to said supporting members, which process comprises forming said filaments to a tolerance such that some of said filaments will be within the said first tolerance and others will be within a second tolerance which differs from the said first tolerance in a manner such that the resultant angular displacement of said leg portions from said first tolerance is in the same direction as would normally occur if the coiled body portions of said filaments were twisted in the direction in which they were wound, completing the fabrication of said filaments, segregating those filaments with leg portions within the limits of the said second tolerance, and then heating the said segregated finished filaments en masse to relieve residual torsional stresses in the coiled body portions thereof and cause said leg portions to swing through an angle suflicient to bring them within the limits of the said first tolerance.

6. The process of aligning the leg portions of coiled refractory wire filaments set forth in claim 5 wherein the segregated finished filaments within the limits of said second tolerance are heated in air at a temperature and for a time sufiicient to effect the desired repositioning of the leg portions without deleteriously oxidizing or embrittling said filaments.

References Cited in the file of this patent UNITED STATES PATENTS 1,013,914 Whitney Jan. 9, 1912 2,142,865 Zabel Jan. 3, 1939 2,163,565 Thomas June 20, 1939 2,219,376 Young et a1 Oct. 29, 1940 2,372,082 Iden Mar. 20, 1945 2,877,804 Greiner et a1 Mar. 17, 1959 

